1. (Field of the Invention)
The present invention relates to a process for improving inner surface properties of plastic resinous tubes by subjecting such inner surfaces to a low-temperature plasma treatment.
2. (Description of the Prior Art)
Prior to filing the present application, it has already been conducted to improve surface properties of plastic resins particularly in hydrophilic and adhesive properties thereof, and also conducted to prevent plasticizers from being eluted, by means of the low-temperature plasma treatment of the surfaces of such plastic resinous goods. Further, it has also been known to conduct polymerization reactions of radical-polymerizable monomers by bringing the same into contact with a plenty of radicals produced on the surfaces of plastic resinous goods which have been subjected to the low-temperature plasma treatment, so as to conduct graft copolymerization reactions on the surfaces of the plastic resinous goods.
It has been known that the process in which the surface graft copolymerization reaction is conducted through such a low-temperature plasma treatment is superior in efficiency and safety to other processes such as processes in which gamma rays, electron rays or ultraviolet rays are irradiated for conducting such reactions, and to a process in which the treatment is conducted with ozone.
In a conventional low-temperature plasma treatment of the inner surfaces of the plastic resinous tubes, the sample is interposed between positive and negative electrodes so that electric discharges are conducted to produce plasma in a space between those electrodes, whereby the inner surfaces of the tubes are treated. Consequently, it is hard to conduct such a treatment efficiently.
Namely, since in the conventional treatment the electric discharge is conducted in a condition in which the electrodes are disposed at opposite ends of the plastic resinous tube, the tube to be subjected to such a treatment are inevitably restricted in length by a distance between the electrodes, and also restricted in number per operation in such a treatment. Those are the disadvantages inherent in the conventional treatment.
Consequently, the conventional process employing the above-mentioned treatment are not suitable for a need for efficiently treating a plenty of such tubes.
In order to solve the above disadvantages, there is proposed a process described in Japanese Patent Laid-Open No. 55-29505 (1980), in which process the tubes are inserted into cylindrical electrodes while the interior of the tubes are kept under a depressurized condition, and low-temperature plasma is produced to make it possible that the tubes are subjected to the low-temperature plasma treatment in the inner surfaces while the tubes are continuously in transit. However, it is technically difficult to uniformly treat the inner surfaces of the tubes by the use of this process. In addition to this disadvantage, such a process is further disadvantageous in that it requires a large-size apparatus provided with a relatively complex mechanism for carrying out the process, while still more gravely disadvantageous in that, since the process requires the electrodes and the treated surfaces to be brought close each other as the other conventional processes do, a rise in tube temperature in process is to an extent which cannot be ignored, resulting in thermal deformations or a formation of concave/convex defects on the treated surfaces.
Since these deformations and defects lead to a grave consequences, for instance, the case where such tubes deter the blood from flowing normally and/or produce a thrombus therein, in case these tubes are employed as medical plastic resinous tubes such as artificial blood vessels. Consequently, the conventional process above is not suitable for producing precise plastic resinous tubes.